The present application claims priority under 35 U.S.C. xc2xa7 119 of Japanese Application No. 2001-362377, filed Nov. 28, 2001, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to thiol compounds, to a method for producing the same, and to an optical product made with the same. The invention generally relates to thiol compounds that may give optical materials having a high refractive index and a high Abbe""s number and having excellent heat resistance and transparency. The invention also relates to a method for producing the same and to an optical product made with the same.
2. Background of the Invention
Plastics are used for various optical applications these days, for example, for lenses and others, as being lightweight, difficult to break, and easily colored when compared with glass. Optical plastic materials include poly(diethylene glycol bisallylcarbonate) (CR-39) and poly(methyl methacrylate). These plastics, however, have a refractive index of 1.50 or less. Therefore, for example, when they are used as lens materials, the lenses produced need to be thicker for increased power, and they lose the advantage of being lightweight. In particular, powerful concave lenses are thick at their periphery, and are therefore unfavorable as causing birefringence and chromatic aberration. For spectacles, such thick lenses are often not aesthetic. To obtain thin lenses, materials with higher refractive index may be used. In general, the Abbe""s number of glass and plastics decreases with the increase in their refractive index, and, as a result, their chromatic aberration increases. Accordingly, plastic materials having a high refractive index and a high Abbe""s number are desired.
Plastic materials proposed as having such properties include, for example, (1) polyurethanes obtained through addition-polymerization of a polythiol having bromine in the molecule and a polyisocyanate (Japanese Patent Laid-Open No. 164615/1983); and (2) polythiourethanes obtained through addition-polymerization of a polythiol and a polyisocyanate (Japanese Patent Publication No. 58489/1992 and Japanese Patent Laid-Open 148340/1993). For the starting material, polythiol for the polythiourethanes of above (2), may be branched polythiols having an increased sulfur content (Japanese Patent Laid-Open Nos. 270859/1990 and 148340/1993), and polythiols into which is introduced a dithiane structure for increasing their sulfur content (Japanese Patent Publication No. 5323/1994 and Japanese Patent Laid-Open No. 118390/1995). Other plastic materials proposed as having such properties include (3) polymers of an alkyl sulfide having a polymerization-functional group, episulfide (Japanese Patent Laid-Open Nos. 71580/1997 and 110979/1997). However, though their refractive index is increased a little, the polyurethanes of (1) above still have a low Abbe""s number and have some other drawbacks in that their lightfastness is poor, their specific gravity is high and therefore, they are not lightweight. The polythiourethanes (2), those for which the starting polythiol used has a high sulfur content, have an increased refractive index of from about 1.60 to 1.68, but their Abbe""s number is lower than that of optical inorganic glass having a refractive index on the same level. Therefore, they still have a problem in that their Abbe""s number must be increased more. On the other hand, one example of the alkyl sulfide polymers (3) having an Abbe""s number of 36 has an increased refractive index of 1.70. The lenses obtained by using this polymer can be extremely thin and lightweight. However, plastic materials having increased Abbe""s number and the refractive index are still desired.
The present invention has been made to address the problems noted above. The present invention provides thiol compounds that may give optical materials having a high refractive index and a high Abbe""s number and having excellent heat resistance and transparency. The present invention also provides a method for producing the same and provides an optical product made with the same.
The present inventors have determined that thiol compounds with mercaptomethyl or mercaptoethyl groups bonded to a 1,3,5-trithiane ring are useful in solving the above-noted problems, and that the compounds may be efficiently produced in a specific method.
Specifically, the invention provides a thiol compound represented by the general formula (1): 
wherein n is 1 or 2.
The invention also provides a method for producing the thiol compound represented by the general formula (1) via an intermediate, i.e., 1,3,5-trithiane having a methylene or vinyl group at the 2,4,6-positions thereof, wherein the groups at the 2-, 4-, and 6-positions may be identical or different.
The particulars shown herein are by way of example and for purposes of illustrative discussion of the various embodiments of the present invention only. In this regard, no attempt is made to show details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
Unless otherwise stated, a reference to a compound or component, includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.
The thiol compounds of the invention may be represented by the general formula (1) mentioned below, from which it is seen that the compound has three mercaptoalkyl groups bonded to the trithiane ring thereof, wherein the mercaptoalkyl groups in a given compound may be identical or different. 
wherein n is 1 or 2.
The trithiane ring of the thiol compound represented by the general formula (1) has a high sulfur content, in which the atomic refraction is high and which therefore significantly increases the refractive index of the polymers obtained by using the thiol compounds of the invention. In addition, the polymerization-functional, terminal thiol groups in the thiol compound contribute toward introducing sulfur atoms into the main chain of the polymers of the compound, and therefore, the refractive index of the polymers obtained by using the thiol compounds of the invention is further increased. In general, the Abbe""s number of amorphous materials is apt to decrease with the increase in the refractive index thereof. One problem with polymers having high sulfur content is that the electron resonance of sulfur is remarkable, therefore often significantly reducing the Abbe""s number. However, the thiol compounds of the invention are free from this problem. Another cause of the increase in the refractive index is the decrease in the molar volume thereof. This is often seen in polymers having a high crosslinking density and a strong intermolecular force. The thiol compounds of the invention have three polymerization-functional groups, and the refractive index of its polymers is increased especially by the former effect. In the general formula (1), the increase in the number n lowers the sulfur content and the crosslinking density, therefore giving polymers having a reduced refractive index. Accordingly, n is generally 1 or 2. In addition, since the glass transition temperature (Tg) of the polymers obtained by using the thiol compounds of the invention lowers with the increase in n in the general formula (1), n is generally 1 or 2 in order to obtain polymers having good heat resistance.
For example, the thiol compound represented by the general formula (1) of the invention includes 2,4,6-tris(mercaptomethyl)-1,3,5-trithiane and 2,4,6-tris(mercaptoethyl)-1,3,5-trithiane.
A method for producing a thiol compound represented by the general formula (1) may comprise forming a 1,3,5-trithiane having methylene or vinyl groups at the 2,4,6-positions thereof, and reacting the 1,3,5-trithiane having methylene or vinyl groups at the 2,4,6-positions thereof to give the thiol compound represented by the general formula (1).
Another method for producing the thiol compound represented by the general formula (1) may comprise the following steps:
(a) reacting chloroacetaldehyde/3-chloropropanal with hydrogen sulfide to obtain 2,4,6-tris(chloromethyl)-1,3,5-trithiane/2,4,6-tris(chloroethyl)-1,3,5-trithiane;
(b) adding a base to remove hydrogen chloride from the compound obtained in step (a) to obtain 2,4,6-trimethylene-1,3,5-trithiane/2,4,6-triethylene-1,3,5-trithiane;
(c) adding thioacetic acid in the presence of a radical generator; and
(d) reducing the S-acetylated compound obtained in step (c) to give 2,4,6-tris(mercaptomethyl)-1,3,5-trithiane/2,4,6-tris(mercaptoethyl)-1,3,5-trithiane.
As a typical example of the method for producing the thiol compound of the invention, synthesis of 2,4,6-tris(mercaptomethyl)-1,3,5-trithiane (a compound of the general formula (1) wherein n is 1) is shown as Scheme 1 mentioned below. Concretely, an aqueous 40 wt. % chloroacetaldehyde solution is dissolved in 70 wt. % sulfuric acid, and hydrogen sulfide is introduced thereinto at xe2x88x9220 to 40xc2x0 C. for 2 to 100 hours to give 2,4,6-tris(chloromethyl)-1,3,5-trithiane. Alternatives to sulfuric acid as the acid solvent include any of 60/40 (v/v) 95 wt. % sulfuric acid-acetic acid, hydrogen sulfide-saturated acetic acid, ether, or 95 wt. % ethanol. To the resulting methanol solution of the thus-formed chlorine compound is added potassium hydroxide with which the chlorine compound is processed at xe2x88x9210 to 40xc2x0 C. for 0.5 to 10 hours for removal of hydrogen chloride from it to give 2,4,6-trimethylene-1,3,5-trithiane. To this compound is added thioacetic acid at 0 to 100xc2x0 C. for 6 to 100 hours in the presence of a radical generator (e.g., 2,2xe2x80x2-azobis(isobutyronitrile), 2,2xe2x80x2-azobis(dimethylvaleronitrile), 4-hydroxycyclohexylphenylketone, and benzoylperoxide), and the resulting S-acetylated compound is then reduced with lithiumaluminum hydride at xe2x88x9210 to 50xc2x0 C. for 0.5 to 6 hours to give 2,4,6-tris(mercaptomethyl)-1,3,5-trithiane (a compound of the general formula (1) wherein n is 1). 2,4,6-Tris(mercaptoethyl)-1,3,5-trithiane (a compound of the general formula (1) wherein n is 2) is obtained in the same manner as above, except that 3-chloropropanal is used in place of chloroacetaldehyde. 
wherein Me is a methyl group.
Optical materials may be obtained by using the thiol compound of the invention. The optical materials are polymers obtained by polymerizing a polymerizable composition that contains at least one component A containing at least the thiol compound (a1) represented by the general formula (1), and at least one component B containing at least one of a compound (b1) having at least two vinyl groups in one molecule, a compound (b2) having at least two iso(thio)cyanate groups in one molecule, and a compound (b3) having at least one vinyl group and at least one iso(thio)cyanate group in one molecule. The iso(thio)cyanate is meant to indicate both an isocyanate and an isothiocyanate.
In addition to the compound (a1) represented by the general formula (1) therein, the at least one component A may additionally contain one or two or more different types of compounds (a2) having a mercapto group and/or a hydroxyl group in one molecule, with the total number of the mercapto group and the hydroxyl group in one molecule being 2 or more, for suitably improving the physical properties of the polymer. Concretely, the compound (a2) includes trimethylolpropane, 1,2-ethanedithiol, 1,3-propanedithiol, tetrakismercaptomethylmethane, pentaerythritol tetrakismercaptopropionate, pentaerythritol tetrakismercaptoacetate, 2-mercaptoethanol, 2,3-dimercaptopropanol, 1,2-dihydroxy-3-mercaptopropane, 4-mercaptophenol, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenedithiol, 1,3,5-benzenetrithiol, 1,2-dimercaptomethylbenzene, 1,3-dimercaptomethylbenzene, 1,4-dimercaptomethylbenzene, 1,3,5-trimercaptomethylbenzene, toluene-3,4-dithiol, and 4,4xe2x80x2-dihydroxyphenyl sulfide. The amount of the compound (a1) represented by the general formula (1) is generally from 0.1 to 100 mole %, and often from 10 to 100 mole % relative to the total amount of the at least one component A.
Examples of the vinyl group-containing compound (b1) for the at least one component B includes divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, as well as urethane-modified (meth)acrylates, epoxy-modified (meth)acrylates and polyester-modified (meth)acrylates each having at least two (meth)acryloxy groups in one molecule. The (meth)acrylate is meant to indicate both acrylate and methacrylate; and (meth)acryloxy group is meant to indicate both an acryloxy group and a methacryloxy group.
Examples of the iso(thio)cyanate group-containing compound (b2) for the at least one component B include xylylene diiso(thio)cyanate, 3,3xe2x80x2-dichlorodiphenyl-4,4xe2x80x2-diiso(thio)cyanate, 4,4xe2x80x2-diphenylmethane diiso(thio)cyanate, hexamethylene diiso(thio)cyanate, 2,2xe2x80x2,5,5xe2x80x2-tetrachlorodiphenyl-4,4xe2x80x2-diiso(thio)cyanate, and tolylene diiso(thio)cyanate. Other examples of the compound (b2) having at least one cyclohexyl ring are bis(iso(thio)cyanatomethyl)cyclohexane, bis(4-iso(thio)cyanatocyclohexyl)methane, bis(4-iso(thio)cyanatomethyl)cyclohexyl)methane, cyclohexane diiso(thio)cyanate, isophorone diiso(thio)cyanate, 2,5-bis(iso(thio)cyanatomethyl)bicyclo[2.2.2]octane, 2,5-bis(iso(thio)cyanatomethyl)bicyclo[2.2.1]heptane, 2-iso(thio)cyanatomethyl-3-(3-iso(thio)cyanatopropyl)-5-iso(thio)cyanatomethyl-bicyclo[2.2.1]heptane, 2-iso(thio)cyanatomethyl-3-(3-iso(thio)cyanatopropyl)-6-iso(thio)cyanatomethyl-bicyclo[2.2.1]heptane, 2-iso(thio)cyanatomethyl-2-[3-iso(thio)cyanatopropyl]-5-iso(thio)cyanatomethyl-bicyclo[2.2.1]heptane, 2-iso(thio)cyanatomethyl-2-(3-iso(thio)cyanatopropyl)-6-iso(thio)cyanatomethyl-bicyclo[2.2.1]heptane, 2-iso(thio)cyanatomethyl-3-(3-iso(thio)cyanatopropyl)-6-(2-iso(thio)cyanatoethyl)-bicyclo[2.2.1]heptane, 2-iso(thio)cyanatomethyl-3-(3-iso(thio)cyanatopropyl)-6-(2-iso(thio)cyanatoethyl)-bicyclo[2.2.1]heptane, 2-iso(thio)cyanatomethyl-2-(3-iso(thio)cyanatopropyl)-5-(2-iso(thio)cyanatoethyl)-bicyclo[2.2.1]heptane, and 2-iso(thio)cyanatomethyl-2-(3-iso(thio)cyanatopropyl)-6-(2-iso(thio)cyanatoethyl)-bicyclo[2.2.1]heptane.
Examples of the compound (b3) having both vinyl and iso(thio)cyanate groups for the at least one component B include 2-(meth)acryloxyethyl iso(thio)cyanate and (meth)acryloyl iso(thio)cyanate. If the at least one component B has a vinyl group, the polymerization-functional groups in the at least one component A may all be mercapto groups. In that case, when the at least one component A has a hydroxyl group, the degree of polymerization does not increase, whereby the mechanical properties of the polymers produced may be reduced.
If desired, the optical materials may contain additives such as UV absorbent, antioxidant, discoloration inhibitor, and fluorescent dye for improving their weather resistance. Also if desired, catalysts may be used for improving the polymerization reactivity. For example, organic peroxides, azo compounds, and basic catalysts are effective for improving the reactivity between the mercapto group and the vinyl group. Organotin compounds and amine compounds are effective for improving the reactivity between the mercapto group or the hydroxyl group and the iso(thio)cyanate group.
If desired, an episulfide compound may be added to these components to fabricate the optical products. Examples of the episulfide compound include linear organic compounds such as bis(xcex2-epithiopropylthio)methane, 1,2-bis(xcex2-epithiopropylthio)ethane, 1,3-bis(xcex2-epithiopropylthio)propane, 1,2-bis(xcex2-epithiopropylthio)propane, 1-(xcex2-epithiopropylthio)-2-(xcex2-epithiopropylthiomethyl) propane, 1,4-bis(xcex2-epithiopropylthio)butane, 1,3-bis(xcex2-epithiopropylthio)butane, 1-(xcex2-epithiopropylthio)-3-(xcex2-epithiopropylthiomethyl)butane, 1,5-bis(xcex2-epithiopropylthio)pentane, 1-(xcex2-epithiopropylthio)-4-(xcex2-epithiopropylthiomethyl)pentane, 1,6-bis(xcex2-epithiopropylthio)hexane, 1-(xcex2-epithiopropylthio)-5-(xcex2-epithiopropylthiomethyl)hexane, 1-(xcex2-epithiopropylthio)-2-[(2-xcex2-epithiopropylthioethyl)thio]ethane, 1-(xcex2-epithiopropylthio)-2-[(2-(2-xcex2-epithiopropylthioethyl)thioethyl)thio]ethane and compounds derived from them by substituting at least one hydrogen of the episulfide group therein with a methyl group; branched organic compounds such as tetrakis(xcex2-epithiopropylthiomethyl)methane, 1,1,1-tris(xcex2-epithiopropylthiomethyl)propane, 1,5-bis(xcex2-epithiopropylthio)-2-(xcex2-epithiopropylthiomethyl)-3-thiapentane, 1,5-bis(xcex2-epithiopropylthio)-2,4-bis(xcex2-epithiopropylthiomethyl)-3-thiapentane, 1-(xcex2-epithiopropylthio)-2,2-bis(xcex2-epithiopropylthiomethyl)-4-thiahexane, 1,5,6-tris(xcex2-epithiopropylthio)-4-(xcex2-epithiopropylthiomethyl)-3-thiahexane, 1,8-bis(xcex2-epithiopropylthio)-4-(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,8-bis(xcex2-epithiopropylthio)-4,5-bis(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,8-bis(xcex2-epithiopropylthio)-4,4-bis(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,8-bis(xcex2-epithiopropylthio)-2,4,5-tris(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,8-bis(xcex2epithiopropylthio)-2,5-bis(xcex2-epithiopropylthiomethyl)-3,6-dithiaoctane, 1,9-bis(xcex2-epithiopropylthio)-5-(xcex2-epithiopropylthiomethyl)-5-[(2-xcex2-epithiopropylthioethyl)thiomethyl]-3,7-dithianonane, 1,10-bis(xcex2-epithiopropylthio)-5,6-bis[(2-xcex2-epithiopropylthioethyl)thio]-3,6,9-trithiadecane, 1,11-bis(xcex2-epithiopropylthio)-4,8-bis(xcex2-epithiopropylthiomethyl)-3,6,9-trithiaundecane, 1,11-bis(xcex2-epithiopropylthio)-5,7-bis(xcex2-epithiopropylthiomethyl)-3,6,9-trithiaundecane, 1,11-bis(xcex2-epithiopropylthio)-5,7-[(2-xcex2-epithiopropylthioethyl)thiomethyl]-3,6,9-trithiaundecane, 1,11-bis(xcex2-epithiopropylthio)-4,7-bis(xcex2-epithiopropylthiomethyl)-3,6,9-trithiaundecane, and compounds derived from them by substituting at least one hydrogen of the episulfide group therein with a methyl group; cycloaliphatic organic compounds such as 1,3- and 1,4-bis(xcex2-epithiopropylthio)cyclohexane, 1,3- and 1,4-bis(xcex2-epithiopropylthiomethyl)cyclohexane, bis[4-(xcex2-epithiopropylthio)cyclohexyl]methane, 2,2-bis[4-(xcex2-epithiopropylthio)cyclohexyl]propane, bis[4-(xcex2-epithiopropylthio)cyclohexyl]sulfide, 2,5-bis(xcex2-epithiopropylthiomethyl)-1,4-dithian, 2,5-bis(xcex2-epithiopropylthioethylthiomethyl)-1,4-dithian, and compounds derived from them by substituting at least one hydrogen of the episulfide group therein with a methyl group; aromatic organic compounds such as 1,3- and 1,4-bis(xcex2-epithiopropylthio)benzene, 1,3- and 1,4-bis(xcex2-epithiopropylthiomethyl)benzene, bis[4-(xcex2-epithiopropylthio)phenyl]methane, 2,2-bis[4-(xcex2-epithiopropylthio)phenyl]propane, bis[4-(xcex2-epithiopropylthio)phenyl]sulfide, bis[4-(xcex2-epithiopropylthio)phenyl]sulfone, 4,4xe2x80x2-bis(xcex2-epithiopropylthio)biphenyl, and compounds derived from them by substituting at least one hydrogen of the episulfide group therein with a methyl group. These compounds may be used either singly or in combination with each other.
Using the thiol compounds of the invention, optical materials can be produced, for example, according to the method mentioned below.
A uniform composition containing the above-mentioned polymerizable composition and other optional additives is first prepared, and this is cast into a glass or metal mold combined with a resin gasket, and heated and cured therein, according to a method of casting polymerization. If desired, the mold may be subjected to mold release or a mold releasing agent such as an acid phosphate ester may be added to the composition, for facilitating good release of the molded resin from the mold. The polymerization temperature varies depending on the compounds to be used, but is generally from xe2x88x9220xc2x0 C. to +150xc2x0 C.; and the polymerization time is from about 0.5 to 72 hours. After having been thus polymerized and released from the mold, the polymer may be readily colored with an ordinary disperse dye in water or in an organic solvent. For facilitating the dyeing, a carrier may be added to the dye dispersion, or the dyeing bath may be heated. Though not limited thereto, the thus-obtained optical materials are especially favorable for optical products such as plastic lenses.
The thiol compounds of the invention have three mercaptoalkyl groups bonded to the center trithiane ring, and are favorable for starting materials for optical materials. The optical materials obtained by using the thiol compounds of the invention have a high refractive index and a high Abbe""s number, and have excellent heat resistance and transparency. Therefore, they are suitable for materials for optical products, for example, for lenses such as those for spectacles and cameras, and also for prisms, optical fibers, substrates for recording media such as optical discs and magnetic discs, as well as for color filters, IR-absorbing filters, etc.